This invention relates to a rubber reinforcing cord suitably used as a reinforcing material of various rubber materials such as tires, belt and hoses, and also to a fiber reinforced rubber material reinforced by said rubber reinforcing cord.
Fiber reinforced rubber materials reinforced by rubber reinforcing cords are widely used as rubber materials such as tires, belts, hoses, etc. In general, in these rubber materials, a matrix containing a rubber is reinforced by a cord obtained by coating a twisted reinforcing fiber bundle with an adhesive to form the surface layer of the bundle.
Carbon fibers have high strength and high elastic modulus and also have excellent heat resistance and water resistance, but are poor in the fatigue resistance against such large deformation as elongation and compression deformation and bending deformation. So, it has been considered that a fiber reinforced rubber material reinforced by a rubber reinforcing cord formed by carbon fibers is poor in durability.
As attempts to solve the problem, JP, 60-181369, A discloses a method of depositing a mixture consisting of an epoxy compound and a rubber latex on a carbon fiber bundle, and JP, 63-6165, A discloses a method of depositing a mixture consisting of a phenol derivative and a rubber latex on a carbon fiber bundle.
However, even these methods cannot satisfy the fatigue resistance required for such rubber materials as tires, belts and hoses, and any rubber reinforcing cord formed by carbon fibers having sufficient fatigue resistance has not be obtained yet.
To solve the above problem, this invention has the following constitution: A rubber reinforcing cord comprising a carbon fiber bundle impregnated with a resin composition comprising a rubber, wherein an elastic modulus of dried film of the rubber at 25xc2x0 C. (Gxe2x80x2) is 0.4 MPa or less , said carbon fiber bundle having a knot-breaking strength of 500 MPa or more.